Variable profile extrusion method

ABSTRACT

An improved method is described for varying the profile as seen in cross section of an elongated extrudate article. The method provides for varying the profile of an extrusion orifice while an extrudate stock material is being forced through the orifice. An elongated extruded article is formed having a varying profile conforming to the variations in the profile of the extrusion orifice.

RELATED APPLICATION

This application is a divisional of prior copending application Ser. No.815,699, filed July 5, 1977, which has issued as U.S. Pat. No. 4,187,068on Feb. 5, 1980.

BACKGROUND OF THE INVENTION

This invention relates to an improved method for extruding articles andto improved products made thereby. The invention relates moreparticularly to the fabrication of an extruded article having a profileas seen in cross section which varies along the length of the article.

The need exists for elongated articles having a cross section or profilewhich varies along the length of the article. More particularly, in thefield of horticulture, for example, it is often desirable to provide ameans for staking saplings and young trees with an elongated stake whichexhibits different requirements with respect to the profile of the stakeat different elevations along its length. A sapling stake is intended tobe inserted into the soil and to securely form an anchor for maintainingthe sapling at a predetermined attitude. A lower segment of the stakeprofile should be tapered to facilitate insertion into the soil, butnearer the surface of the soil it should exhibit substantial lateralprojected area and cross-sectional dimensions in order to resist lateraldisplacement in the soil to establish a firm anchor in the soil andcorresponding relatively greater strength, i.e. greater section modulus,to resist the maximum bending moment which occurs near the soil surface.On the other hand, a resilience or predetermined flexibility in thatsegment of the stake above the soil is desired to enable the sapling toflex somewhat during its growth under varying atmospheric conditions. Astake having these differing requirements can be provided by varying theprofile of the sapling stake along its length and by fabricating it of amaterial which exhibits a memory characteristic.

When a sapling is supported by unduly rigid stakes, its trunk is notallowed to flex in a natural manner under wind loads. The result is thatthe trunk of the tree does not develop proper strength for supportingitself under heavier wind loads later on in its life. By suitablytapering the stake a predetermined flexural resilience is provided whichtends to match the natural flexibility of the tapering trunk of thesapling. Thereby, the sapling is allowed to flex naturally in alldirections under ambient wind conditions. Its trunk develops appropriatestrength, and a healthier young tree results when the stake support isremoved. In addition to sapling stakes, other articles such as fenceposts and the like have differing profile requirements at differentelevations along its length. Further desirable characteristics for thesearticles which are generally maintained outdoors are a resistance tocorrosion, fungus, and to decay.

Prior articles intended at least partially to satisfy these requirementshave been fabricated of metal or of wood. Metal fence post or stakearticles have been formed by the usual well known metal fabricatingtechniques, and have been relatively expensive, have not exhibited thedesired resilience, and are subject to corrosion over a period of timein an outdoor environment. Alternatively, articles of this type arefabricated by woodworking techniques and are conventionally of uniformcross-sectional area, thus being unmatched to the tapering trunk of asapling. They do not provide the desired flexural resilience andgenerally do not exhibit the desired overall strength and weatheringcharacteristics. Moreover, wood stakes of uniform cross-sectional areaoften do not provide sufficient lateral projected area at the soilsurface and within the soil. Accordingly, if the soil becomes softenedby rain, the stake may readily become displaced laterally and tilt over.Furthermore, unless specially treated, they are readily susceptible todecay and to rot.

These articles may be formed of thermoplastic polymer materials whichexhibit the desirable memory, resistance to corrosion and which are notsusceptible to decay, fungus and to rot. However, thermoplastic polymerarticles are generally fabricated by extrusion or by injection molding.In prior extrusion techniques, a plastic stock material in plasticizedor in a liquid form is forced through a die having an orifice of fixeddimensions and having a desired profile or cross-sectionalconfiguration. The article thus extruded has a substantially uniformprofile along the entire length of the extruded section.

With respect to injection molding, which involves high pressures, forexample, such as 20,000 pounds per square inch, the fabrication ofelongated stake or fence post articles requires relatively large, strongexpensive dies for injection molding presses. In addition, it is oftennot possible to produce some of the articles by injection moldingbecause of the need for complex, multiple parting lines in the injectionmolding die to enable stripping of the product from the molds. Thus,articles having undercuts or multiple fins, for example, could not bestripped from the die without damaging the articles.

Accordingly, it is an object of this invention to provide a method forextruding an elongated article having a variable profile along itslength.

Another object of this invention is to provide an elongated articleformed of a polymer plastic and having a variable profile along thelength of the article.

Still another object of the invention is to provide an elongated articleof the type described having mechanical characteristics of relativerigidity and relative flexibility at different locations along thelength of the article.

SUMMARY OF THE INVENTION

In accordance with features of the method of this invention, anelongated article having a profile which varies along the length of thearticle is fabricated by forcing an extrudate stock material inplasticized or liquid form through an orifice which is formed by aplurality of extrusion die members defining an orifice profile. Theposition of at least one of said members is varied while forcing thestock material through the orifice thereby varying the profile of theorifice and forming an elongated extrudate having a varying profilewhich conforms to the varying profile of the orifice. In accordance withother features of the method of the invention, the position of aplurality of the extrusion die members is varied intermittently orcontinuously in an extrusion cycle during which an elongated extrudedarticle is formed.

In accordance with features of the apparatus of this invention, a dieblock assembly means is provided having a plurality of die block membersand an extrusion orifice formed therein by the members. The orifice hasa periphery establishing an orifice profile which is defined by edgesegments of the plurality of die block members. A means is provided forforcing an extrudate stock material through the orifice to form anelongated extrudate article having a profile conforming to the profileof the orifice. A means is also provided for automatically varying aposition of an edge segment of at least one of the die block members forvarying the profile of the orifice as the stock material is forcedtherethrough. An elongated extrudate article having a varying profile isthus provided.

In accordance with other features of the invention, an elongatedextrudate article formed of thermoplastic polymer material and having aprofile which varies along the length of the article is provided. Thearticle comprises, for example, a sapling stake, a post or other similararticle which exhibits the desired resistance to outdoor environment andwhich is fabricated without the use of relatively expensive injectionmolding forms and dies.

Examples of other articles which can be made to advantage using thepresent invention are trim strips or decorative moldings having changingprofiles to provide attractive scalloped, serrated or other formed edgesor surfaces. Such trim strips may be used for home decoration, both inthe interior or exterior. They may be applied on gable ends, eaves,soffits, and so forth, to provide a finished appearance. At the presenttime, such trim strips and moldings are commercially available asunpainted lengths of wood which have been machined to shape. The usermust paint and maintain these decorative wood items to resistweathering. Care in installation to avoid splitting or breaking away ofdelicate cross-grain contours is required.

It is among the advantages of the present invention that such variableprofile decoractive trim strips can be extruded continuously withrelatively low tooling costs in pre-colored and finished appearance inreadiness to be cut into 8, 10, 12 or 16 foot lengths, as may be desiredfor marketing. They are durable and do not require the maintenance whichis associated with wood trim. Furthermore, commercially available woodtrim strips and moldings can exhibit undesired variations in machiningtechniques from length-to-length, or even several noticeable changes inpattern along various regions of the same strip. In marked distinctionto such problems, variable profile extrudate articles produced inaccordance with the present invention are produced under controlledconditions to provide predetermined repeatability of the desiredpatterns with consistent quality and pre-finished appearance ready forinstallation.

Other types of articles which can be produced to advantage by employingthis invention are tapered, multi-faceted furniture legs, fancybanisters and dowels, and the like. As compared with wood from whichsuch furniture parts and decorative dowels have conventionally beenproduced, there are the same kinds of advantages as discussed above ofconsistent quality, durability, attractive pre-finished appearance andlack of grain. Although such furniture parts and decorative dowels maybe injection molded in certain cases, the present invention enables themto be produced at a lower tooling and lower production costs.

In addition, the present invention enables changes in variable contoursand stylized patterns to be made relatively quickly and easily withshort "down time" and low changeover costs. Consequently, articles ofelongated shape subject to low volume production, runs of multiplepattern styles, can be produced economically.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the invention will becomeapparent with reference to the following specification and to thedrawings wherein:

FIG. 1 is a side elevational view of a sapling stake of varying profileconstructed in accordance with features of this invention;

FIG. 2 is an enlarged view of a cross section taken along the lines 2--2of FIG. 1, being a cross section at an elevation near the surface of theearth when the stake is installed in use;

FIG. 3 is an enlarged view of a cross section taken along the lines 3--3of FIG. 1, being a cross section at an elevation which is more than halfof the way up along the stake above the location of the section shown inFIG. 2;

FIG. 4 is a front elevational view of a post of varying profileconstructed in accordance with features of this invention;

FIG. 5 is a side elevational view of the post of FIG. 4;

FIG. 6 is an enlarged view of a cross section taken along lines 6--6 ofFIG. 4;

FIG. 7 is an enlarged view of another cross section taken along thelines 7--7 of FIG. 4;

FIG. 8 is a fragmentary view of a portion of a die assembly for formingthe post of FIG. 4 and constructed in accordance with the features ofthis invention;

FIG. 9 is a front elevational view of an extrusion die constructed inaccordance with the features of this invention and illustrating the dieorifice profile for the stake of FIG. 1 at its maximum profile;

FIG. 10 is a front elevational view, partly in section, of the extrusiondie of FIG. 9 and illustrating the die orifice profile for the stake ofFIG. 1 at its minimum profile;

FIG. 11 is a view taken along the lines 11--11 of FIG. 10;

FIG. 12 is a front elevational view, partly in section, of an extrusiondie constructed in accordance with an alternative embodiment of theinvention;

FIG. 13 is an alternative arrangement for a die profile actuating meansof FIG. 12; and

FIG. 14 illustrates a further alternative arrangement for a die profileactuating means of FIG. 12.

DETAILED DESCRIPTION

Referring now to FIGS. 1-7, elongated articles having a varying profilealong their length and which are formed of a polymer plastic areillustrated. The plastic material used is thermoplastic, as for examplehigh density polyethylene, polyvinyl chloride, polypropylene, and otherthermoplastic materials can be used having the desired properties forthe particular end use application involved. A sapling stake 20, shownin FIGS. 1-3, has a varying profile. For the purpose of thisspecification and the appended claims, the term profile means thecross-sectional configuration or the cross-sectional area of an article.In FIG. 2, the stake is shown to have a central segment 22 and finsegments 24, 26 and 28 which extend in a radial direction from thecentral segment 22. The profile of the stake 20 varies from a maximum ata location 30 along its length to minimum cross-sectional areas at thelocation 32 and 34 along its length. The sapling stake provides desiredcharacteristics, as enumerated hereinbefore, since it includes a segmentextending from location 30 to 34 which is tapered to facilitateinsertion into the soil and, at the same time, provides substantialstrength and rigidity for anchoring the stake in the soil.

In further explanation, the location 30 is at an elevation along thestake when it is installed in the soil which is near the surface of thesoil. The fin segments 24, 26, 28 extend laterally outward and therebyprovide a relatively large projected area as seen from any lateraldirection. This large projected area is embedded in the soil andstrongly resists lateral displacement of the stake in the soil, evenwhen the soil may be soft or spongy after a severe rainstorm. Inaddition, the section modulus of the stake 20 has a maximum value at theelevation 30 which is intended to be near the soil surface. It is at thesoil surface where the bending moment of applied loads on the installedstake are greatest. Consequently, the stake 20 advantageously exhibitsits maximum flexural stiffness and strength where the maximum bendingmoment is applied to it.

On the other hand, the profile of the stake varies continuouslyproviding a continuous tapering length segment 31 from the location 30to the location 32 which is at an elevation more than half of the way upthe stake from the location 30 of maximum section modulus. This changingprofile provides various lengths of the stake with a resilientcharacteristic enabling saplings and other larger plants which aresecured thereto a degree of flexure during growth and adverse weatherconditions.

By virtue of the fact that the stake 20 tapers over the major portion ofits exposed length above the soil surface from location 30 to location32, it provides a progressively changing flexural resilience which tendsto match the natural flexibility of the tapering trunk of the sapling.As explained above, allowing the trunk of the sapling to sway naturallyunder incident wind loads occurring from day-to-day from the differentcompass directions advantageously causes the growing trunk to developstrength analogous to the result that appropriate exercise strengthensthe limbs of an animal. Fabrication of the stake from a stiffly flexiblepolymer plastic provides a memory characteristic so that the resilientdeflection of the stake length between locations 30 and 35 thereofresults in the restoration of the stake to an undeflected attitude uponremoval of the deflecting force.

In a particular embodiment, the sapling stake 20 is formed ofthermoplastic polymer material, for example such as translucentpolypropylene or high density polyethylene, and has an overall length ofapproximately 81/2 feet. The lower portion of the stake varies inprofile from the lower tip 34 to the location 30 of maximum sectionmodulus and is approximately 18 inches long. The next portion 31 variesin profile from the location 30 to the location 32 and is approximately48 inches long. The upper portion 37 from the location 32 to the top 35is of constant profile and, for example may have a length of 36 inches.The fins 24, 26 and 28 along this upper portion 37 may each be notchedslightly to form a set of notches. Such sets of notches may be providedat several different elevations along the upper portion 37 to preventlongitudinal slippage of the cord, twine, fabric strips or bands whichmay be used to support a sapling from the stake 20 at one or severalelevations along the trunk of the sapling. For example, there may be sixsets of such notches spaced approximately six inches apart in elevationalong the upper stake portion from 32 to 35.

Also, as an illustrative example, the central segment 22 of the stake isshown as being round in section having a radius of approximately 3/16thsof an inch. Each of the fin segments 24, 26 and 28 has a thickness ofapproximately 1/4th of an inch. Its outer surface is rounded in asemi-circle, as seen in FIGS. 2 and 3, which has a radius ofapproximately 1/8th of an inch, thereby further protecting the saplingbark from abrasion or scuffing injury. In FIG. 3, the distance from theaxial center of the stake to the point on the centerline of each finsegment at the outer surface thereof is approximately 5/16ths of aninch. In other words, at the elevations 32 and 34 each of the finsegments 24, 26 and 28 protrude 5/16ths of an inch from the axialcenterline of the stake 20. At the elevation 30 of maximumcross-sectional area, as shown in FIG. 2, each of the fin segmentsprotrudes 1/2 of an inch from the axial centerline of the stake.

Furthermore, this sapling stake 20 is advantageously formed oftranslucent plastic material, as indicated above, at least in portions31 and 37 which are intended to project above the ground. A tree,particularly a sapling, tends to grow away from a dark shadow. Thus,when supported from a wood stake, or a metal pipe, the sapling tends togrow away from the supporting object. This tendency is undesirablebecause the tree starts out growing somewhat crooked as a result of theshadow effect of the supporting object, resulting in a less attractiveor weaker tree than if the trunk were straight and truly vertical. Byvirtue of the fact that the stake 20 is translucent, for example havingan overall pale, milky appearance, light is allowed to pass through thestake and shadow effects are markedly lessened, thereby encouraging thesupported sappling to grow straight up along beside a stake which isessentially "invisible" to the young growing tree.

The fence post 36 of FIGS. 4-7 is similarly an elongated body having avarying profile, as illustrated by the differences in thecross-sectional area of the profile at the location 37 and at thelocation 38. There is a tapering length segment of the post 36, asrepresented by that portion of the post extending from the location ofthe lower shoulder 39 to its lower tip or distal end 40. There is also atapering length segment of the fence post extending from the location ofthe upper shoulder 44 up to the location 42. It will also be noted inFIG. 5 that a fin segment 46 has a serrated configuration. Theserrations 48 with intervening teeth enable the positive non-sliplocating and securing of the tie wires, fence lines or fence mesh andthe like at desired locations along the length of the post.

This fence post has a wide rear fin segment 41 opposite to the narrowserrated front fin segment 46. This rear fin segment 41, as seen in FIG.5, is of uniform width along its length, except that it tapers from itsshoulder 39 down to the tip 40 for ease of driving into the soil. Thistaper at the lower end of the uniformly wide rear fin 41 can readily beformed by cutting a triangular piece off from this fin after thevariable profile extrusion operation to produce the fence post 36 hasbeen completed. There are two side fin segments 43 and 45 which arerelatively wide in the regions between their shoulders 39 and 44, asshown also by the cross-sectional configuration seen in FIG. 6. Thesewide portions of the fin segments 43 and 45 are intended to be embeddedin the soil for providing a large projected area, as seen in the lateraldirection, to resist displacement of the fence post in the soil even ifthe soil is softened by rain. Also, the section modulus of the fencepost 36 is greatest in the region between the shoulders 39 and 44 wherethe bending moments caused by the pull of the fence are greatest.

Since both the post 36 and the sapling stake 20 are formed of a polymerplastic, they exhibit a desirable resistance to deterioration and arenot susceptible to decay, rot, rust, corrosion and fungus althoughutilized primarily in outdoor environments. Moreover, the plasticmaterial provides smooth surfaces which will not splinter to causepiercing injuries to trees or people and will not corrode or scale offto cause rough bumps which injure hands and create rubbing injury orgirdling damage to the tree bark. The plastic material will not supportinsect life or parasites.

An apparatus for forming elongated extrudate articles having a varyingprofile, such as the stake 20 and the post 36, is illustrated in FIGS.8-11. As schematically indicated in FIG. 8, the fence post 36 may bevariable profile extruded by an extrusion orifice 47 defined by a fixeddie block 49 and a plurality of movable die members 51, 53 and 55. Thestructure and mounting of the movable die members 51, 53 and 55 and theway in which they may be moved radially inwardly and outwardly incontrolled cycles will become understood from the following descriptionof an embodiment of the variable profile extrusion method and apparatusfor producing the sapling stake 20.

A means for providing an extrudate stock material in plasticized orliquid form is provided and is shown to include a heated extruder barrel50 (FIG. 11) and means 52 for feeding the plastic material forward inthe barrel, for example such as an extruder screw which rotates withinthe barrel 50. The extrudate stock in pellet or powder form iscontinuously drawn from a hopper (not shown) into the heated barrel bythe action of the rotating screw 52 where it is heated to plasticized orliquid form 33 and is forced at high pressure through a rounded exitport or aperture 54 located at the mouth of the barrel 50. A heatedmaster die plate 60 is mounted to a flange 56 (FIG. 11) surrounding themouth of the barrel by screw means 61 which extend through bores 62 inthis flange and engage internally threaded bores 63 in the plate 60. Themaster die plate 60 includes a throat aperture 64, having an axis 65therein, which is centrally formed in the plate and communicates withthe extruder barrel aperture 54. Extrudate stock material is forcedthrough the aperture 64 and then through an extrusion orifice, discussedhereinafter.

Since the viscosity of the stock extrudate is an importantcharacteristic in the extrusion process and is dependent upon itstemperature, the master die plate 60 is heated by a plurality ofresistance heaters (FIG. 10) 66, 67, 68, 70, 72 and 74. These arethermostatically controlled in accordance with the desired temperatureof the plate as determined by a temperature sensing element 76 (FIG.10). Although a plurality of such temperature sensing elements will beprovided, only one such element is illustrated for purposes ofsimplifying the drawing. During an extrusion process, it is alsodesirable to monitor the pressure of the extrudate. To this end, achannel 78 (FIG. 11) communicates with the aperture 64 and a pressuresensing element 80 is positioned therein which generates an electricalsignal proportional to the extrudate pressure.

The master die plate 60 provides a support for variable profileextrusion die means referred to generally by reference numeral 90 andfor a cam 92. It is to be noted that the master die plate 60 andassociated variable profile extrusion die means 90 are shown asrelatively massive in structure with a multiplicity of heaters 66, 67,68, 70, 72 and 74 for providing ample heating capacity. The relativelymassive and well heated structure provides a good thermal conductivitythroughout itself for maintaining all of the extrusion die parts atessentially the same uniform temperature. The thick master die plate 60serves as a backing or mount of good thermal conductivity for the diemeans and thereby enhances the desired tendency to maintain temperatureuniformity throughout all die parts affecting the temperature of thethermoplastic material being extruded. In addition, this relativelymassive mounting plate and die structure 60, 90 of good conductivityprovides a thermal flywheel effect which resists variations in localizedtemperature in the thermoplastic extrudate. Thus, the temperature of theplastic material is maintained substantially constant to achieve good,uniform flow characteristics in spite of variations frommoment-to-moment of volumetric flow through the die orifice, as occurswith changes in cross section of the extrudate.

The mounting plate 60 also provides a pivotal mount for a cylindersupport bracket 93 of a pneumatic return cylinder 96 which serves as aspring for causing the die means 90 to follow the motion of the cam 92,as will be explained. The cam 92 is driven by a shaft 114 to whichrotary motion is imparted by a motor (not shown) which is energized inaccordance with a predetermined program for actuating a member of thedie extrusion means 90. A bore 116 is formed in a bracket segment 118 ofthe plate 60 and a cam shaft rotary bearing 120 is positioned in thebore. Another bracket segment 122 of the plate 60 supports the cylindermounting bracket 93. A spacer pivot mount 126, having a threaded shank128, is provided for supporting the cylinder 96 at a spaced apartposition from the plate 60. The threaded shank 128 of mount 126 engagesan internally threaded bore 130 formed in the bracket segment 122 whilean opposite end of the mount extends as a pivot through a bore 132(FIGS. 9 and 10) in the cylinder bracket 93 and provides a pivotalmounting for this cylinder. Means, such as a cap nut or cotter pin (notillustrated) are provided for maintaining the pivot 126 in engagementwith the bore 132.

The extrusion die means 90, referred to hereinbefore, comprises aplurality of die block members which form an extrusion orifice. At leastone of the die block members is movable. In FIG. 10, the die blockmembers are shown to comprise an annular shaped stationary member 140and a plurality of movable members 142, 144 and 146. The stationary dieblock member 140 includes a plurality of radially extending grooves 148,150 and 152 formed therein in which the movable members 142, 144 and 146are positioned respectively and which provide rectilinear guides forthese members.

The plurality of die block members form an orifice which is referred togenerally by reference number 154 and which has a periphery outlining anorifice profile. This periphery and the orifice profile are defined byedge segments 156, 158 and 160 of the stationary die block member 140and by edge segments 162, 164 and 166 of the movable die block members142, 144 and 146, respectively. The annular stationary die block member140 includes an annular flange 168 (FIG. 11) extending from a surface170 and engaging an annular groove 172 formed in the master die plate60. The flange 168 and the groove 172 enable alignment of the stationarydie block member 140 with the plate 60 thereby aligning and locating anaxis 180 of the orifice 154 with the axis 65 of the master die plate 60.

A means for varying the position of an edge segment of at least one ofthe die block members and thus the profile of the orifice 154 as stockextrudate material is forced through this orifice, is provided andincludes an annular shaped actuator ring 191, the cam 92 and its drive,the cylinder 96, and drive means providing engagement between the ring191 and the movable die member. The actuator ring 191 is positioned onand rotates about a bearing surface 192 of the stationary die blockmember 140. A lip 194 formed in the actuator ring limits axial movementof the ring 191 in a first axial direction relative to the stationarydie block member 154. A cam follower surface 195 (FIG. 10) is providedon a bracket 196 of the ring and is engaged by a peripheral surface 198of the cam 92. The ring also includes an integrally formed extendingbracket 199 having a pin 200 supported therein for engaging a bore 202formed in an end bracket 204 of the piston rod 206.

The stationary die block 140, the movable die block members 142, 144 and146 located in grooves of the stationary die block 140 and the rotaryactuator ring 191 comprise a die assembly which is mounted to the masterdie plate 60 by an annular shaped retainer ring 208 (FIG. 9) and aplurality of screws 210-220. These screws extend through a plurality ofbore holes in the plate 208 as exemplified in FIG. 11 by the bore 222through which the screw 210 extends, and through a plurality ofcorresponding bores in the stationary die block 140, as exemplified bythe bore 224. These screws engage a plurality of associated internallythreaded bores in the master die plate 60, as exemplified by theinternally threaded bore 225 in this plate. As shown in FIG. 11, aperipheral lip 209 on the retainer ring plate 208 overlaps the interiorlip 194 of the movable actuator ring 191 for preventing the ring 191from moving in the downstream direction.

Radial inward and outward movement of the movable die block members 142,144 and 146 is effected by rotation of the actuator ring 191. Thepneumatic cylinder 96 biases the actuator ring 191 in a clockwisedirection as viewed in FIG. 10 since the cylinder member bracket 93 iscoupled to the stationary bracket 122 while the piston rod 206 iscoupled to the bracket 199 which is integral with rotatable ring 191. Apneumatic pressure is initially established for creating this clockwisebias of the ring 191. As the cam 92 rotates, it forces the cam followersurface 195 and the ring 191 to rotate in a counterclockwise directionagainst the biasing pressure within the cylinder 96. This pressuremaintains the follower surface 195 against the cam surface 198 andthereby turns the ring 191 in a clockwise direction as permitted bymotion of the cam surface.

During an extrusion cycle, the movable die block members are advanced ina radial direction toward the axis 180 of the orifice 154 therebyvarying the orifice profile for decreasing the width of the finsegments, as viewed in FIG. 10, during one portion of an operatingcycle, or are retracted away from the axis 180 in a radial direction forvarying the orifice profile for increasing the width of the finsegments, as viewed in FIG. 9, at another position of the operatingcycle. This movement is effected by rotary motion of the actuator ring191. A plurality of grooves 230, 232 and 234 are formed in the actuatorring 191 thereby providing control cams for controlling the respectivepositions of the movable die block members 142, 144, 146, as will beexplained later.

Each of the movable die block members, as exemplified by the die blockmember 144 in FIG. 11, is generally L-shaped in the radial plane andincludes an orifice forming inner edge segment in the form of a firstleg 164 of the L-shape, and a radially outwardly extending stem segment236 forming a second leg of the L-shape. A pin 238 is press fitted intoa bore 240 formed in a lower portion of the second leg 236 of theL-shape. A roller or bearing sleeve 242 is positioned about the pin 238.This assembly of the pin 238 and the roller bearing 242 extend into thegroove 230 formed in the actuator ring 191. Similar cam follower pin androller assemblies 250, 251, 252, 253 (FIG. 10) are positioned in othercam grooves 232 and 234 of the actuator ring. It can be seen that thegrooves 230, 232 and 234 are each inclined in the radial direction forproviding that the respective ends of these inclined cam grooves arelocated at a different radial distance from the axis 180 of the orifice.Thus, upon rotation of the actuator ring 191, the inclined cam grooveswill cause the cam follower assemblies 238, 242; 250, 251; and 252, 253of the movable die members to move in a radial direction with respect tothe axis 180 of the orifice 154. The edge segments of the movable dieblock members are caused to advance or retract correspondingly, and theprofile of the orifice is thereby varied. The particular movement of theedge segments of the movable die block members and thus the profile ofthe orifice will be determined during an extrusion cycle by theconfiguration of the cam 92 and by the configuration of the cam grooves230, 232 and 234.

As seen in FIG. 11, the fixed die block 140 has a streamlined convergententry region 255 extending downstream from the entry face of orifice154. Similarly, each of the movable die block members, as exemplified bythe movable die block member 144, has a streamlined convergent entryregion 257 extending downstream from this entry face. These streamlinedconvergent regions 255 and 257 guide the extruding plastic material 259to flow unimpeded into the die orifice 154 without upstreamdisturbances.

As shown in FIG. 11, in order to allow for the escape of any plasticmaterial which may force itself outwardly along the outwardly extendingside surfaces of the stem portion 236 of the movable die block member144, there is a small bleed port 263 in the retainer cover ring plate208. This bleed port 263 communicates with the clearance space 261outside of the inner segment 164 of the movable die block member 144.Similar bleed ports 263 (as seen in FIG. 9) are provided for thecorresponding clearance spaces of the other movable die block members142 and 146. A small amount of plastic material 259 can be seen issuingfrom the bleed port 263.

For producing the sapling stake 20, an extrusion cycle will be completedafter the cam 92 makes one full revolution. During this movement of thecam, the extruder screw 52 is continuously forcing stock extrudatematerial in plasticized or liquid form from the extruder barrel 58,through the master die plate aperture 64 and through the orifice 154. Anelongated article having a cross sectional profile corresponding to theprofile of the orifice 154, as it is varied during the cycle, will thusbe extruded through the orifice 154. An elongated article having avarying profile along its length is thereby provided during oneextrusion cycle. Extrusion is generally continuous and a plurality ofarticles will thus be formed, which can subsequently be cut from oneanother to complete the finished article.

In addition to the apparatus illustrated in FIGS. 9, 10 and 11 of thedrawings for providing the extrudate article, various other known meansemployed in an extrusion apparatus including extrudate stock hopper,heating means for the extruder barrel, cooling bath means for theextrudate, and extrudate puller means which are well known in theextrusion arts are employed but are not illustrated for purpose ofsimplifying the drawings and the description thereof.

The variable profile extrusion method and apparatus thus describedexhibits several advantages. In addition to providing the desiredvariable profile for an extruded article, the assembly of dies, actuatorring and cam is readily mounted and demounted for substituting variousdifferent arrangements of die members in order to effect variousdifferent profile configurations. It will be noted from the drawingsthat the rotary actuator ring, the stationary and movable die blockmembers, and the cam can be readily demounted by the steps ofdisengaging the mounting screws 210-220 and the piston rod from the pin200. Thus, the apparatus described is versatile in that various dieblock members adapted to provide desired profiles can be readilysubstituted.

FIG. 12 illustrates an alternative means for rotating an actuator ring299 during an extrusion cycle. As can be seen from FIG. 12, the profileof the article being extruded has a T-shaped configuration. The T-shapedprofile can be altered in that the length of the stem fin segment 300can be varied by movement of a die block member 302, while the thickness304 of the head of the T can be altered by movement of the die blockmember 306. The die block member 302 is actuated by a cam followerassembly 308 located in an inclined cam groove 310. This cam followerassembly 308 is similar to the cam follower assemblies 238, 242; 250,251; and 252, 253 shown most clearly in FIG. 10. The movable die blockmember 306 is actuated by movement of two cam follower assemblies 312and 314 which extend into a pair of identical inclined cam grooves 316and 318, respectively. Because of the relatively large radial forcesexerted during the extrusion process on the relatively large die surface307 of the movable die block member 306, this movable die block memberis provided with the dual cam follower assemblies 312 and 314 acting inconcert for transmitting the actuating force to this member at twoseparate places spanned across its relatively large width.

It is to be understood that the movable die block members 302 and 306cooperate with the stationary die block member 140A in a manneranalogous to that shown and described in detail in conjunction with FIG.9. The machine screws 210-218 serve to secure the variable profile diemeans 90A to a corresponding master die plate 239 which is generallysimilar to the master die plate 60 as shown in FIG. 11. The variableprofile die orifice 154A communicates with an aperture corresponding tothe aperature 64 (FIG. 11).

In FIGS. 9-11, movement of the actuator ring 191 was effected by themechanical transmission of an actuating torque to the ring 191 from thecam 92 via the cam follower surface 195 while the restoring torque onthis ring was provided by the pneumatic cylinder 96 acting on a movablearm 199.

In FIG. 12, rotary movement of the actuator ring 299 during an extrusioncycle is accomplished by hydraulic cylinders 320 and 322, a springloaded hydraulic tracer valve 324 which is mounted on and rotated withthe ring 299 and by a cam 325. Brackets 326 and 328 of the hydrauliccylinders 320 and 322, respectively, are pivotally mounted to a masterdie plate 329 by pins 330 and 332, respectively. Piston rods 334 and 336are coupled to bracket segments 338 and 340 of the actuator ring 299 bypins 342 and 344, respectively. The piston rods are coupled to the ring299 at different circumferential locations in push-pull torquerelationship for producing a powerful driving torque on the rotary ringin each respective direction when the hydraulic cylinders 320 and 322are appropriately pressurized.

An hydraulic fluid 350 is supplied from a reservoir 352 via a pump 354and a conduit 356 to the tracer valve 324. A hand operated by-passpressure-relief valve 355 is provided in parallel circuit relationshipwith the pump 354 for relieving any excess pressure which might occurdownstream of the pump. The tracer valve 324 which is actuated by thecam 325 distributes the hydraulic fluid 350 under pressure through aconduit 358 for causing clockwise rotation of the ring 299, as viewed inFIG. 12, or to a conduit 360 for causing counterclockwise rotation ofthe ring. The hydraulic fluid under pressure in the conduit 358 iscoupled to the hydraulic cylinders 320 and 322 by flexible branch lines361 and 359 for causing extension of the piston 334 from the cylinder320 and simultaneous retraction of the piston 336 into the cylinder 322,thus providing a powerful push-pull effect in exerting clockwise torqueon the rotatable ring 299. Similarly, the hydraulic fluid under pressurein the conduit 360 is distributed to the cylinders 320 and 322 byflexible branch lines 363 and 365 for causing retraction of the piston334 into the cylinder 320 and extension of the piston rod 336 from thecylinder as illustrated in FIG. 12. Thus, powerful counterclockwisetorque is exerted on the rotatable ring 299.

The use of dual hydraulic cylinder means for actuation of the ring 299enables the application of relatively higher die actuation forces thanis provided with the cam drive arrangement of FIGS. 9-11. It alsoresults in balancing the torque forces being applied on the oppositesides of this ring and the reaction forces of the driven cam followerassemblies 308, 312 and 314, thereby minimizing frictional effectsduring the actuation of the movable die members in a variable profileextrusion process.

The advantageous actuation of the hydraulic cylinders through the use ofa control cam 325 which is not bearing any significant load and a tracerroller 362 operating the tracer (or servo) valve 324 enables relativelyabrupt changes in cylinder control motion and rapid changes in theprofile of extruded articles. The cam 325 may be rotated by anyconvenient source of rotary motion applied to its shaft 367 which isjournalled in a bracket 369 on the master die plate 329. The spring 371in the tracer valve 324 biases the valve spool plunger 373 toward theright in FIG. 12 and maintains the follower roller 362 in contact withthe revolving cam surface 325.

Thus, when the valve spool 373 moves to the right of its neutralposition, it causes the hydraulic cylinders 320 and 322 to produceclockwise rotation of the actuator ring 299. When the valve spool is inits neutral position, it causes the actuator ring 299 to be heldtemporarily stationary. When it moves to the left of neutral position,it produces counterclockwise rotation of the actuation ring.

The hydraulic fluid returns through either of the conduits 358 or 360,as the case may be, and is discharged through a valve passage 375 and aline 377 returning to the reservoir 352.

It is to be noted that the tracer valve 324 is mounted on a bracket 379extending from the periphery of the rotatable ring 299. Therefore, themovement of the valve spool plunger relative to the housing of thetracer valve 324 is a resultant of the action of the cam 325 plus theaction of the movable bracket 379. Consequently, fairly rapid andcomplex variations in profile of the orifice 154A can conveniently beproduced.

At times it may be desirable to provide even more rapid changes inpositioning of the actuating ring 299. While the arrangement of FIG. 12enhances such movement, relatively quick changes in the position of theactuating ring are limited to some extent by the ability of the tracerroller 362 to follow the profile and ramp angles of the control cam 325.In FIG. 13, there is illustrated an apparatus for further multiplyingand amplifying the amplitude and slopes of the cam configuration with atracer valve mechanical lever linkage which accomplishes relativelyquicker and multiplied response of the actuator ring 299 for veryrapidly varying the profile of the extruder die.

In FIG. 12, the tracer valve 324 is supported on an arm 379 on theactuator ring 299 and was transported therewith during its rotarymotion, as discussed above. In the arrangement of FIG. 13, the tracervalve 324 is supported on a lever arm 364 of a lever system 366 forminga mechanical linkage for coupling the tracer valve in an articulatedmanner to the periphery of the rotatable ring 299. This arm 364 ispivotally supported by a fixed pivot 368 at an elbow region 370 of thelever linkage 366. A coupling slot 372 is formed at the end of anotherlonger arm 374 of the lever 366, and a pin 376 which is secured to abracket 378 near the periphery of the ring 299 engages in the slot 372.

Thus, relatively small movements of the servo valve 324 causemechanically multiplied movements of the rotatable actuator ring 299,depending upon the relative lengths of the two lever arms 364 and 374.The servo valve plunger 373 is advantageously enabled to follow the camprofile in spite of relatively rapid or abrupt movements of the actuatorring 299. Moreover, the angular attitude of the axis of the valveplunger 373 relative to the axis of the cam shaft 367 changes as the arm364 swings about the pivot 368 for providing various control effects. Asa result, the tracer valve is permitted to accomplish relatively morecomplex, varied higher speed and larger amplitude control actions inproducing the resultant movement of the extrusion die members andaccordingly to provide relatively more abrupt, repeatable and complexvariations in the article profile as desired.

At times, a linear cam profile rather than an annular cam profile may bedesired for actuating the tracer valve 324. FIG. 14 illustrates anarrangement for linear actuation of this valve. A longitudinally movablecam plate 380 is provided having a first ramp 382 of relatively steepslope and a second ramp 384 of relatively less steep slope. The tracerroller 362 is maintained in engagement with the edge 385 of the camplate which is reciprocated within a track or groove 386 of a fixedsupport frame 388. The linear cam plate 380 is actuated by a piston rod390 of a pneumatic cylinder 392 mounted on the support 388.

This linear cam arrangement can be used to provide the same generalpattern of variable profile extrusion as the annular cams of FIGS. 9-13.The ramp segments 382 and 384 can be adapted to have equivalentprofiles, if desired, in which case the cam plate 380 can bereciprocated in opposite directions at the same rate to provide the samevariable profile. In other words, each extension and each retraction ofthe piston rod 390 can be arranged to produce a complete operatingcycle, if desired.

If it is desired to produce two lengths of elongated articles having thesame relative proportions in the same production run, the cam plate 380can be driven back and forth in opposite directions at different speeds.Thus, an alternating sequence of relatively longer and shorter articlesof varying profile are produced as a continuous extrusion. They are thencut apart from each other and are ready for marketing.

It is to be understood that when using the motion amplifying leverlinkage 366 on FIG. 13 the hydraulic connection for causing retractionand extension of the piston rods 334 and 336 are reversed from those asshown in FIG. 12; so that the valve 324 will continue to operate as aservo valve. Thus, when the valve spool 373 moves to the right of itsneutral position in FIG. 13, it produces counterclockwise rotation ofthe actuator ring 299, thereby causing the lever arm 364 and the valve324 to move toward the right. When the valve spool 373 is in its neutralposition, it causes the actuator ring to be held temporarily stationary.When it moves to the left of its neutral position, it produces clockwiserotation of the actuator ring, thereby causing the lever arm 364 and thevalve 324 to move toward the left. The movement of the servo valve 324is much less than the multiplied movement of the actuator ring 299.

If desired, a lever system similar to that shown in FIG. 13 can beemployed for moving the servo valve 324 in FIG. 14. The connections tothe hydraulic cylinders should always be such that the valve 324 in FIG.14 will operate as a servo valve. Thus, when the cam follower 326 movesto the right of its neutral position in FIG. 14, the servo valve 324should move to the right, and vice versa.

There has thus been described an improved method for fabricating animproved elongated extruded article of variable profile. Althoughparticular embodiments of the invention have been described herein, itwill be apparent to those skilled in the art that variations may be madethereto without departing from the spirit of the invention and the scopeof the appended claims.

I claim:
 1. A method for extruding an elongated article having a profilewhich remains the same in at least one radial direction along its lengthand which may be varied in at least three other radial directions alongits length comprising the steps of:forming an orifice in a fixed diemember which is stationary in at least one radial direction and whichmay be varied in at least three other radial directions using aplurality of movable extrusion die members, forcing a thermoplasticextrudate stock material in flowable form through said orifice, andvarying the position of at least two of said movable die members whileforcing said stock material through said orifice thereby maintaining theprofile the same in at least one radial direction while simultaneouslyvarying the profile of the orifice in at least two other radialdirections for forming an elongated extrudate article having a constantprofile in at least one radial direction and a varying profile in atleast two radial directions conforming to the varying profile of saidorifice.
 2. The method of claim 1, wherein said article is formed duringan extrudate forming cycle and the position of said members is variedcontinuously during said cycle.
 3. The method of claim 1, wherein saidarticle is formed during an extrudate forming cycle and the position ofsaid members is varied during a part of said cycle.
 4. The method ofclaim 1, wherein the positions of at least three members are variedwhile forcing said stock material through said orifice.